1. Field of the Invention
The present invention relates to a method of forming a chalcogen compound thin film, and more particularly to a method of forming a chalcogen compound thin film, which is suitable for use in a light-absorption layer of a solar cell.
2. Description of the Related Art
Recently, the importance of the development of next-generation clean energy has increased due to serious environmental pollution and the depletion of fossil fuels. A solar cell is a device that directly converts solar energy into electric energy. The solar cell induces little pollution, includes a material obtained from an infinite resource, and has a semipermanent life span, and accordingly, the solar cell is expected to be an energy source that solves future energy problems.
The solar cell is classified into various types, depending on the material that is used in a light-absorption layer. Currently, the most frequently used solar cell is a silicon solar cell using silicon. However, there is growing interest in a thin-film solar cell due to currently rapidly increasing cost of silicon attributable to the short supply thereof. Since the thin-film solar cell is manufactured to be slim, a small amount of material is used, and the application range thereof is extensive due to its low weight. Examples of a material used in practice, among the materials of the thin-film solar cell, include CdTe. Recently, CIGS (copper indium gallium selenide), having a high light-absorption coefficient, has come into the spotlight.
Among the materials that are used, CdTe and CIGS have drawbacks in that In, Ga, and Te are costly materials and Se and Cd are toxic.
In order to overcome the drawbacks, there is continued interest in novel materials for a light-absorption layer. Among the materials, SnS has a band gap (1.1 eV) which is similar to that of silicon. However, since its light-absorption coefficient is much larger than that of silicon, SnS may absorb most of the sunlight spectrum in a range that is larger than the band gap, even when SnS is formed to a thin film having a thickness of 1 μm or less. Tin and sulfur are general elements, reserves thereof are abundant, and Tin and sulfur are not toxic.
The efficiency of an SnS thin film-based solar cell has remarkably improved from 1.3% to 4.36% in the last two to three years. Efficiency is relatively low when using a thermal evaporation process but is best when using an ALD process. However, there is a drawback in that the ALD process is difficult to apply industrially. The SnS solar cell has not yet been commercialized due to the costly process of forming the SnS thin film.